Planar magnetrons have long been used by the semiconductor processing industry in sputtering devices to coat silicon wafers with various materials, for example aluminum, during the manufacture of integrated circuits.
A sputtering device with a stationary planar magnetron is typically a high rate sputtering device which represents an enormous improvement over devices based on diode sputtering or evaporative techniques. However, a sputtering device with a stationary planar magnetron has practical shortcomings, the most serious of which is that the plasma discharge erodes a narrow groove in the target. This localized erosion generates a non-uniform distribution of sputtered atoms which results in a deposition on the semiconductor wafer having non-uniform step coverage.
Numerous attempts, some partially successful, have been made to modify such a source to extend the target erosion and to make the distribution of sputtered atoms more uniform. For example, U.S. Pat. No. 4,444,643, which is incorporated herein by reference, describes a sputtering device which includes a mechanically rotated permanent magnet assembly. The rotation of the permanent magnet assembly causes erosion over a wider area of the target.
Other attempts have been made to spread out the erosion over a larger surface area using extended magnetic fields. The magnets required for such an approach are large and complicated, and it is difficult to assure that the properties of the magnetron do not change as the target erodes away. The resulting erosion pattern is thus difficult to predict.
Special arrangements of the magnets have also been suggested for producing more uniform erosion. One such arrangement is described in European Patent Application Publication No. 211,412 entitled Magnetron Sputtering Apparatus and its Magnetic Source, published Feb. 25, 1987. Another such arrangement is described in Japanese Patent Application Publication (Kokai) No. 62-211,375 entitled Sputtering Apparatus, published Mar. 11, 1986. As is discussed in this disclosure, our work shows that neither of these suggested arrangements will produce uniform erosion.